1. Field of the Invention
The invention relates to frame rate up-conversion (FRUC) technique, and more particularly, to a circuit and method for calibrating motion vectors for periodic patterns.
2. Description of the Related Art
Frame rate up-conversion (FRUC) is the conversion process between any two display formats with different frame rates. FRUC has various applications, e.g., saving bandwidth in low bit-rate video transmission, reducing movies juddering in converting a 24 fps video source into a higher frame rate and reducing blurring effect in a hold-type liquid crystal display (LCD).
Most FRUC use motion estimation (ME) to obtain motion vectors of moving objects and then perform motion compensated interpolation (MCI) to interpolate images of the moving objects in different frames. Most ME methods calculate motion vectors with the minimum sums of absolute difference (SAD) according to block matching estimation (BME) algorithm. However, under certain circumstances, many ME methods are inclined to fall in the trap of the local minimum SAD value. That is, a motion vector with the local minimum SAD value is not necessarily the real motion vector of a moving object; furthermore, even a motion vector with the global minimum SAD value is not necessarily the real motion vector of the moving object.
Most video sources contain periodic patterns like windows of buildings, text strings and striped clothes, etc. FIG. 1 shows an example of a periodic pattern. Referring to FIG. 1, a feature of periodic patterns is that periodic patterns usually contain plural local minimum SAD value in its SAD map. Thus, even though a motion vector MV1 with the global minimum SAD value is found according to the conventional MBE algorithm, the motion vector MV1 is not necessarily the real motion vector of the periodic pattern. FRUC is proposed to obtain better image quality. However, wrong motion vectors will degrade interpolated images and make it uncomfortable for watching experience.